The invention relates to a method for generating microlithographic images with polarized light and a projection exposure system.
A method and an arrangement of the above kind are disclosed in U.S. Pat. No. 6,191,880 and the references cited therein.
The radial polarization suggested in U.S. Pat. No. 6,191,880 for objectives having a typical image end numerical aperture NA=0.5 to 0.7 and a resist without an antireflection coating is well suited for suppressing disturbances caused by the polarization-selective reflection on the resist at angles of incidence in the region of the Brewster angle.
U.S. Pat. Nos. 5,365,371 and 5,436,761 disclose the arrangement of polarization-selective means for radial polarization also in the pupil plane (system aperture) of the projection objective.
U.S. Pat. No. 5,691,802 discloses a catadioptric projection objective wherein a polarization plate is arranged in the pupil plane of the projection objective. This plate has an inner circular zone and an outer annular zone which generate linearly polarized light mutually orthogonal and, at the same time, have different indices of refraction. In this way, two non-interfering light beams are provided which generate different image planes. A relationship to the kind of illumination is not provided. The numerical aperture of the given examples is at most 0.6.
U.S. Pat. No. 4,755,027 discloses axicon arrangements for the generation of radially as well as tangentially polarized light.
It is an object of the invention to provide a method and corresponding arrangements which are optimized with respect to polarization effects for a further increased image end numerical aperture from approximately 0.7 to 0.9 and greater.
The interference contrast becomes determining for antireflection coated resist (light-sensitive coating in the image plane) and further increased image end numerical aperture NA. This interference contrast is optimal when there is two-beam interference for beams having a polarization orientated perpendicular to the plane of incidence (sagittal, "sgr"). A contrast increase of approximately 7% is, for example, possible in this way.
The method of the invention is for microlithographically generating an image with polarized light including the step of providing light beams which incident in an image plane and causing the light beams to interfere to form an image in the image plane; and, imparting a polarization to the light beams to have a preferred direction of the polarization orientated perpendicular to the incidence plane.
The projection exposure system of the invention for microlithography includes: a light source for supplying light along an optical axis; an illumination arrangement defining an illumination aperture and being disposed on the optical axis downstream of the light source; the illumination arrangement including: a first component for influencing the polarization of the light by generating more than 60% of tangential polarization of the light; and, a second component for determining the illumination aperture; a mask positioning device on the optical axis downstream of the illumination arrangement; a projection objective defining an image plane and being arranged on the optical axis downstream of the illumination arrangement; and, an object positioning device disposed on the optical axis downstream of the projection objective.
According to another feature of the invention, a ring aperture illumination or dipole illumination is provided. According to the invention, such a polarization is made available in the illumination and is maintained in the beam path. With ring aperture or dipole illumination, the potentials of high numerical aperture and the polarization according to the invention are optimally utilized.
This polarization has to be maintained in the further beam path.
For the case of a catadioptric reduction objective, the arrangement of the invention provides, after the last mirror on the image side, an arrangement which influences the polarization in accordance with the adjusted geometry of the pupil illumination and effects a tangential polarization of the light beams contributing to the image formation.
Tangential polarization is suitable for annular aperture illumination as well as for dipole illumination.
According to another feature of the invention, linear polarization is also suitable for dipole illumination and this linear polarization is to be rotated with the dipole direction.
The invention is not advantageous with quadrupole illumination.
Interventions into the illumination system are easier than into the reduction objective and, for this reason, the tangential polarization is made available in the illumination system. This polarization should then be maintained in the reduction objective. It is therefore advantageous when the projection objective (reduction objective) is configured to be rotationally symmetrical in the beam path and especially as a refractive objective or an axial symmetric catadioptric objective. The axially symmetrical catadioptric objective is disclosed, for example, in U.S. Pat. No. 6,169,627.
To optimize the uniform polarization in the image plane, it is advantageous when disturbance influences (in series manufacture or specific to a particular unit) of the optical elements, which follow the arrangement which influences the polarization, are corrected in anticipation so that these disturbances are compensated in the image plane.
According to a feature of the method of the invention, a polarization neutral microlithographic mask is provided so that the polarization, which is generated at the illumination end, is not disturbed. Especially preferred are transmission masks having a substrate which is not double refracting in the passthrough.
According to another feature of the invention, an anti-reflection coating of the light-sensitive resist of the wafer to be exposed is provided because otherwise the light couples into the layer with too low an intensity at the high angles of incidence which correspond to the numerical aperture in the range from 0.7 to 0.9 and above.
According to another feature of the invention, this anti-reflection coating can be optimized especially for the light, which is polarized perpendicularly to the incidence plane, and this is a significant simplification compared to the otherwise required optimization for all polarization directions.